Contact lenses made from silicone-containing materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Regardless of their water content, both non-hydrogel and hydrogel silicone contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
Those skilled in the art have long recognized the need for modifying the surface of such silicone contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of the contact lens surface improves the wettability of the contact lenses. This in turn is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens's susceptibility to deposition, particularly the deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended wear lenses, the surface is especially important, since extended wear lens must be designed for high standards of comfort over an extended period of time, without requiring daily removal of the lens before sleep. Thus, the regimen for the use of extended wear lenses would not provide a daily period of time for the eye to recover from any discomfort or other possible adverse effects of lens wear.
Silicone lenses have been subjected to plasma surface treatment to improve their surface properties, e.g., surfaces have been rendered more hydrophilic, deposit resistant, scratch resistant, or otherwise modified. Examples of previously disclosed plasma surface treatments include subjecting contact lens surfaces to a plasma comprising an inert gas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942; and 4,214,014); various hydrocarbon monomers (see, for example, U.S. Pat. No. 4,143,949); and combinations of oxidizing agents and hydrocarbons such as water and ethanol (see, for example, WO 95/04609 and U.S. Pat. No 4,632,844). U.S. Pat. No. 4,312,575 to Peyman et al. discloses a process for providing a barrier coating on a silicone or polyurethane lens by subjecting the lens to an electrical glow discharge (plasma) process conducted by first subjecting the lens to a hydrocarbon atmosphere followed by subjecting the lens to oxygen during flow discharge, thereby increasing the hydrophilicity of the lens surface.
Although such surface treatments have been disclosed for modifying the surface properties of silicone contact lenses, the results have been problematic and of questionable commercial viability, which has no doubt contributed to the fact that silicone hydrogel contact lens have yet to be commercialized. For example, U.S. Pat. No. 5,080,924 to Kamel et al. states that although exposing the surface of an object to plasma discharge with oxygen is known to enhance the wettability or hydrophilicity of such surface, such treatment is only temporary.
Although the prior art has attempted to show that the surface treatment of contact lenses in the unhydrated state can be accomplished, there has been little or no discussion of the possible effect of subsequent processing or manufacturing steps on the surface treatment of the lens and no teaching or description of the surface properties of a fully processed hydrogel lens manufactured for actual wear. Similarly, there has been little or no published information.
Thus, it is desired to provide a silicone hydrogel contact lens with an optically clear, hydrophilic surface film that will not only exhibit improved wettability, but which will generally allow the use of a silicone hydrogel contact lens in the human eye for extended period of time. In the case of a silicone hydrogel lens for extended wear, it would be highly desirable to provide a contact lens with a surface that is also highly permeable to oxygen and water. Such a surface treated lens would be comfortable to wear in actual use and would allow for the extended wear of the lens without irritation or other adverse effects to the cornea. It would be desirable if such a surface treated lens were a commercially viable product capable of economic manufacture.